Orthopedic Screw and Porous Structures Thereof

ABSTRACT

A bone fastener includes a head, and a screw portion extends from the head. The screw portion includes a shaft and a thread extending along and about the shaft. The thread has a height extending from a root to a tip thereof. The thread also has first and second portions disposed between the root and the tip. The second portion has a porous structure configured to promote bone ingrowth and has a porosity greater than that of the first portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/263,068, filed on Jan. 31, 2019, which claims the benefit of thefiling date of U.S. Provisional Patent Application No. 62/625,541, filedFeb. 2, 2018, the disclosure of which is hereby incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to bone screws and more particularly tobone screws having a partially porous structure for promoting bonegrowth therein.

BACKGROUND OF THE INVENTION

Bone screws are utilized in a wide variety of orthopedic applicationsincluding procedures in which the bone screws are used to reduce bonefragments or to connect one or more structures to a bone. In thisregard, it is desirable for such bone screws to maintain theirrespective positions within a bone for extended periods of timeincluding for the life of the patient. While certain existing bonescrews may be utilized with plates, implants or the like that employback-out prevention features, there exists a continued need for improvedfixation within the bone.

BRIEF SUMMARY OF THE INVENTION

The present disclosure describes exemplary embodiments of bone screwsthat include both solid and porous portions. The porous portions ofthese screws promote bone ingrowth to help facilitate long term fixationof such screws, while the solid portions provide structural support.Moreover, the solid and porous portions each comprise an exterior ofeach of the described screws such that the solid and porous portionscome in contact with bone when applied thereto. In this regard, theratio of bone contacting surface area defined by the porous portionsrelative to that of the solid portions may be predetermined such thatthe amount of bone growth into the porous portions is controlled so thatthe removal torque of the screw can be overcome by ordinary surgicalinstruments even after ingrowth has occurred over an extended period oftime in order to remove the screw from the bone without having to cutthe bone surrounding the screw. The bone screws described herein may bemade via an additive manufacturing process, which can allow the porousportions to be disposed in locations on the screw difficult orimpossible to achieve by other manufacturing processes and so that theporous and solid portions are integrated with each other to form aunitary/monolithic screw.

In one aspect of the present disclosure, a bone fastener includes ahead, and a screw portion extending from the head. The screw portionincludes a shaft and a thread extending along and about the shaft. Thethread having a height extending from a root to a tip thereof. Thethread also having first and second portions disposed between the rootand the tip. The second portion includes a porous structure configuredto promote bone ingrowth and having a porosity greater than that of thefirst portion.

Additionally, the height of the thread may increase toward a distal endof the bone fastener. Also, the shaft may taper inwardly toward thedistal end of the bone fastener. The first portion of the thread may bepositioned further from the shaft than the second portion. Moreover, thefirst portion and the second portion may collectively define an outerbone contacting surface of the thread, and the first portion may have asolid structure.

Continuing with this aspect, a height of the second portion may beconstant along a length of the shaft. Also, a height of the firstportion may increase toward a distal end of the bone fastener. Theheight of the thread may include the heights of the first portion andsecond portion. A height of the second portion may be about 0.5 mm orgreater. The head, shaft and first portion of the thread may eachcomprise a solid structure that has a porosity smaller than that of thesecond portion.

In another aspect of the present disclosure, a bone fastener includes ahead, and a screw portion extending from the head. The screw portionincludes a shaft and a thread extending helically along and about theshaft and defines a helical depression therebetween. The screw portionalso includes a plurality of porous fenestrations disposed within thehelical depression and extends into the shaft. The porous fenestrationsare filled with a porous structure configured to promote bone ingrowth.The porous structure includes a portion of an external surface of thebone fastener and is surrounded by a solid structure having a porositysmaller than that of the porous structure. Also a porous liner at leastpartially surrounds the channel and is disposed within the shaft of thescrew portion. The porous liner includes a porous structureinterconnected within the porous structure of at least two of the porousfenestrations.

Additionally, the porous fenestrations may each define a circularopening having a diameter of 0.5 to 1.2 mm. 12. The porous fenestrationsmay extend into the shaft 0.5 mm or greater. The bone fastener mayfurther include a channel extending along the length of the bonefastener and through both the screw portion and head of the bonefastener. At least some of the porous fenestrations may extend throughthe shaft and into communication with the channel such that the porousstructure extends from the channel to an exterior of the bone fastener.

Continuing with this aspect, each porous fenestration may be offset froman adjacent porous fenestration by 10 to 90 degrees about a longitudinalaxis of the bone fastener. Each porous fenestration may be offset froman adjacent porous fenestration by 20 degrees about a longitudinal axisof the bone fastener. A bone fastener may include a head, first andsecond screw portions each including a shaft, and a thread extendingalong and about the shaft. A shank may be disposed between the first andsecond screw portions. The shank may be threadless and having aplurality of porous portions interspersed within a solid substrate suchthat an exterior surface is both solid and porous. The plurality ofporous portions may be a plurality of fenestrations that extend into thesolid substrate of the shank and may be filled with a porous structurethat is configured to promote bone ingrowth. The fenestrations may behelically arranged about the shank. The porous fenestrations may eachdefine a circular opening having a diameter of 0.5 to 1.2 mm. 21 Theporous portions may extend into the solid substrate about 0.5 mm orgreater.

In a further aspect of the present disclosure, a bone fastener includesa screw portion having a shaft and a thread, and a head positioned at aproximal end of the screw portion. The head includes a proximal portionand a distal portion. The distal portion of the head defines a bonecontacting surface that faces in a direction toward a distal end of thescrew portion. The distal portion has a porous structure configured topromote bone ingrowth and has a porosity greater than that of theproximal portion and the screw portion. The distal portion of the headdefines a porous ring that extends about a longitudinal axis of the bonefastener.

Additionally, the porous structure of the distal portion may extendpartially into a solid structure of the head. The head may be tulipshaped and may have a slot extending through the head in a directiontransverse to a longitudinal axis of the screw, the slot may beconfigured to receive a spinal rod therein. The head may include athreaded inner surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, aspects, and advantages of the present invention willbecome better understood with regard to the following description,appended claims, and accompanying drawings in which:

FIG. 1A is a perspective view of a bone screw according to an embodimentof the present disclosure.

FIG. 1B is a perspective view of a head of the bone screw of FIG. 1A.

FIG. 1C is a schematic view of a thread of the screw of FIG. 1A.

FIG. 1D is a cross-sectional view of the bone screw of FIG. 1A takenalong a midline thereof.

FIG. 2A is a perspective view of a bone screw according to anotherembodiment of the present disclosure.

FIG. 2B is a cross-sectional view of the bone screw of FIG. 2A takenalong a midline thereof.

FIG. 3 is a perspective view of a bone screw according to a furtherembodiment of the present disclosure.

FIG. 4 is a perspective view of a bone screw according to an evenfurther embodiment of the present disclosure.

FIG. 5 is a perspective view of a bone screw according to yet anotherembodiment of the present disclosure.

DETAILED DESCRIPTION

As used herein, when referring to the disclosed devices, the term“proximal” means closer to the operator or in a direction toward theoperator and the term “distal” means more distant from the operator orin a direction away from the operator. Also, as used herein, the terms“about,” “generally,” and “substantially” are intended to mean thatslight deviations from absolute are included within the scope of theterm so modified.

FIGS. 1A-1D depict a cannulated bone screw 100 according to anembodiment of the present disclosure. Bone screw 100 generally includesa head 110, screw portion 120 extending from head 110, and a channel 130extending through screw portion 120 and head 100. Such channel 130 maybe configured to receive a k-wire and/or a flowable material such asbone cement, medicament, bone marrow aspirate, and the like. However, insome embodiments, screw 100 may not include channel 130.

Head 110 includes an underside 112 and a topside 114. Underside 112defines a first radial surface 115. Topside 114 includes an upwardextending post 113 and a plurality of downwardly extending grooves 111(see FIG. 1B) positioned about post 113. Such grooves 111 are adapted toengage a complementary driver tool. However, other configurations forengaging a driver tool that are known in the art are contemplated. Post113 defines a second radial surface 117 that has a radius smaller thanthat of first radial surface 115. In this regard, head 110 is a dualradius head which is configured to be driven by a driver while alsobeing configured to polyaxially anchor other components to a bone, suchas a stabilizing rod and coupling element to a vertebra. Examples ofscrews similar to screw 100, as well as components, such as stabilizingrods, coupling elements, and drivers, that can be used in conjunctionwith screw 100 are disclosed in U.S. Pat. Nos. RE42,932; 6,488,681;7,686,834; 8,231,635; RE45,338; and 9,408,716, the entireties of whichare incorporated by reference herein and all of which are assigned tothe same entity as the present invention. However, it is to beunderstood that the present invention can be utilized in a connectionwith any type of screw designed to be implant into bone.

Screw portion 120 extends distally from head 110 and includes a shaft128, helical thread 122, distal tip 129, and one or more cutting flutes127. Shaft 128 extends from head 110 and tapers inwardly toward a distalend of screw 100. Shaft 128 also defines a minor diameter of screw. Inthis regard, the minor diameter of screw 100 gradually decreases in adistal direction. Distal tip 129 extends distally from shaft 128 and isalso tapered in the distal direction. As depicted distal tip 129 isthreadless. However, in some embodiments distal tip 129 may be fully orpartially threaded. Cutting flutes 127 may extend along both shaft 128and distal tip 129 to facilitate self-tapping. However, in someembodiments, particularly those that are not self-tapping, screw 100 maynot include a cutting flute.

Thread 122 of screw 100 helically extends along and about shaft 128.Thread 122 has a height (h) defined between a root 123 and a crest 121of thread 122, as depicted in FIG. 1C. Thread 122 has a single start anddefines a major diameter of screw 100. However, in some embodiments,screw 100 may include multiple threads defining multiple starts. In theparticular embodiment depicted, the major diameter is constant along thelength of the majority of shaft 128. Thus, because the taper of shaft128 and the constant outer diameter of thread 122, the root 123 to crest121 height (h) of thread 122 increases in a distal direction, as is bestshown in FIG. 1D. However, it should be understood that screw 100 mayhave other configurations, such as a constant minor diameter and avariable major diameter, or a constant major and minor diameter.

Thread 122 includes a first portion 124 and a second portion 126 betweenroot 123 and crest 121. First portion 124 and second portion 126 arepositioned adjacent each other with first portion 124 positioned furtherfrom shaft 128 than second portion 126. In this regard, first portion124 is positioned at a radial extent of thread 122 and defines crest121. Second portion 126 is positioned adjacent to shaft 128 at a base ofthread 122. However, at a distal end of thread 122 near the start ofthread 122, first portion 124 may not be positioned over second portion126, as shown in FIG. 1A.

First portion 124 has solid structure, while second portion 126 has aporous structure. The porous structure of second portion 126 has aporosity that promotes bone ingrowth over time when tissue is in contacttherewith, as well as to aid in initial fixation prior to ingrowth. Forexample, the porous structure of second portion 126 may have an averagepore diameter between 20-1000 microns with a 30-80% porosity. However,preferably the porosity may be between 55-65% and may either be constantthroughout the porous structure or gradient such that the porousstructure has a varying porosity. In contrast, the solid structure offirst portion 124, to the extent it may have a porosity, does not have aporosity that promotes bone ingrowth and has therefore has a porosityless than that of the porous structure of second portion 126 andgenerally no porosity whatsoever. However, the solid structure of firstportion 122 provides strength and stability to thread under differentloading conditions. The remainder of screw 100 other than thread 122,which includes head 110, shaft 128, and distal tip 129, may have a solidstructure similar to that of first portion 124 of thread 122. The porousportions of screw 100, as well as the solid portions thereof, may beformed through use of an additive manufacturing process as describedbelow, and may be made from the same material or different material thatis capable of bonding with each other through the additive manufacturingprocess.

Porous second portion 126 has a constant height along the length ofshaft 128. As mentioned above, the root-to-tip height (h) of thread 122increases in the distal direction. Thus, since porous second portion 126of thread 122 has a constant height along the length of shaft 128, solidfirst portion 124 of thread 122 has a variable height along the lengthof shaft 128, as best seen in FIG. 1D. In this regard, the height offirst portion 124 decreases in the proximal direction. In otherembodiments of screw 100, porous second portion 126 may have a variableheight along the length of shaft 128 while solid first portion 124 has aconstant height. In even further embodiments of screw 100, first andsecond portions 124, 126 of thread 122 may each have variable heightsalong the length of shaft 128. However, it is preferable that that theheight of porous portion 126 be about 0.5 mm or greater.

Porous second portion 126 and solid first portion 124 comprise a bonecontacting surface that is therefore both porous and solid. In thisregard, solid first portion 124 helps provide strength while screw 100is driven into bone and porous second portion 126 facilitates boneingrowth at opposite sides of thread 122 to promote long term fixationof screw 100 and to prevent inadvertent backout thereof during theperiod of time that screw 100 is implanted. However, it may be necessaryat some point to remove screw 100 from the bone even after extendedperiods of time over which bone ingrowth has occurred. In this regard,the surface area of porous structure of second portion 126 that isexposed to bone is proportional to or smaller than that of the surfacearea exposed to bone of the solid structure 124 so that the resistanceafforded by bone ingrowth can be overcome through torsion applied toscrew 100 using standard driver instruments. In one embodiment of screw100, height “h” of thread 122 may be 50% comprised of the porous secondportion and 50% of the solid first portion. In other embodiments, theheight “h” of thread 122 can comprise 10% to 90% of the surface area ofthread.

In a method of use, a driver is engaged to topside 114 and screw 100 isdriven into bone, such as a vertebrae. As screw 100 is driven into thebone, solid first portions 124 of thread 122 and thread flute 127 cutthrough the cortical and cancellous layers of the bone. Once fullyseated, the natural roughness of porous second portion 126 of threads122 may help prevent backout of screw 100 via frictional resistance.Thereafter, implantable equipment may be connected to screw 100, such ascomponents of a spinal rod system or a bone plate for fracture reductionand stabilization, for example. Over time, bone may grow into porousstructure 126 of screw 100 helping to further secure screw 100 to thebone. If after a such ingrowth occurs it is necessary to remove screw100 from the bone via a revision procedure or the like, screw 100 may bereengaged with a driver instrument and rotated such that the bondsformed between screw 100 and bone via bone ingrowth are broken therebyallowing screw 100 to be removed without the need to cut excess bonesurrounding screw 100 for its removal.

FIGS. 2A and 2B depict a screw 200 according to another embodiment ofthe present disclosure. Screw 200 is similar to screw 100 in that screw200 includes a head 210, screw portion 220 extending from head 210, anda channel 230 extending through screw portion 220 and head 100. Inaddition, head 210 is similar to head 110 in that it includes a topside214 that defines a post 213 and plurality of grooves 211 for engaging acorresponding driver and an underside 212 that defines a radial surface215 with a radius larger than a radial surface 217 of post 213. Also,screw portion 220 includes a shaft 228, thread 222, and distal tip 229similar to that of screw 100. However, screw 200 differs with respect toits solid and porous configuration.

As shown, screw 200 includes a plurality of porous fenestrations 226that extend into shaft 228 from an outer surface thereof and in ahelical arrangement between thread 222. In other words, thefenestrations are positioned in a helical depression that is defined bythread 222. Each fenestration 226 may be positioned at a predeterminedangle relative to adjacent fenestrations 226. For example, eachfenestration may be distributed every 10 to 90 degrees in a helicalpattern about screw 200 and relative to each adjacent fenestration 226,but preferably every 20 degrees. Fenestrations 226 are depicted asdefining round openings in the solid structure of shaft 228, which mayhave a diameter 0.5 to 1.2 mm, but preferably 1 mm. However,fenestrations 226 can define various different shaped openings, such asrectangular, ovular, triangular, and the like, for example. Porousfenestrations 226 are filled with a porous structure such that theporous structure forms a portion of an external surface of screw 200 atthe respective openings of porous fenestrations 226. As described below,porous fenestrations 226 provide strength to screw 200 relative to acomplete absence of structure in fenestrations 226 and allows for boneingrowth into its porous structure and for injection of materialstherethrough, such as bone cement, bone marrow aspirate, and biologics.

In addition to porous fenestrations 226, screw 200 includes one or moreporous liners 227 lining channel 230. Such porous liners 227 may befully cylindrical so as to form a sleeve that has an opening coaxialwith channel 230. However, in some embodiments, porous liners 227 may bepartially cylindrical and thus may not encircle channel 230. In thisregard, liners 227 along with the solid structure of shaft 228 definechannel 230. Liners 227 extend along at least a portion of shaft 228 ofscrew portion 220 and may extend between a plurality of fenestrations226. Porous liners 226, as shown, do not extend entirely through theradial extent of shaft 228. However, porous liners 226 are preferably incommunication with some or all of porous fenestrations 226. In thisregard, a flowable material such as bone cement and medicament can beinjected through channel 230, porous liners 227, and selectedfenestrations 226 so that the bone cement or medicament can be deliveredto the bone from multiple locations along the length of screw 200.Alternatively, bone marrow aspirate can be aspirated from the bone frommultiple locations along the length of screw 200. Even further, bonegraft material can be packed into channel 230 to bolster bone ingrowth.

While porous liners 227 are depicted in FIG. 2B as affordingcommunication of porous fenestrations 227 with channel 230 of screw 200,it is also contemplated that screw 200 may not have porous liners 227and instead each porous fenestration 226 or a select number thereof mayextend entirely through shaft 228 so as to communicate directly withchannel 230. In this regard, porous fenestrations 226 may form a uniformcolumn of porous material that extends entirely through shaft 228.

The porous structure of liners 227 and fenestrations 226 is similar tothat previously described for promoting bone ingrowth. Additionally, insome embodiments, the porous structure in each fenestration 226 may havethe same porosity, while in other embodiments the porosity may differfenestration-by-fenestration. Moreover, the porosity in eachfenestration 226 may be uniform or it may differ such that the porosityof each fenestration 226 increases in an outwardly radial direction. Inaddition, the remaining features of screw 200 other than porousfenestrations 226 and liners 227 are comprised of a solid structure soas to reinforce screw 200 and provide strength to screw 200 as well asto help control the surface area ratio between the porous and solidstructure to allow for bone ingrowth that can be overcome by apredetermined amount of torque applied to screw 200.

In a method of use, a driver is engaged to topside 214 and screw isdriven into bone, such as a vertebrae. As screw 200 is driven into thebone, the solid thread 222 cuts into the cortical and cancellous layersof the bone. Once fully seated, bone cement or medicament may beinjected or, alternatively, bone marrow aspirated, through channel 230and porous fenestrations 226 to treat the bone or provide additionalfixation support thereto such as described in U.S. application Ser. No.15/286,039, the disclosure of which are hereby incorporated by referencein their entireties herein. Also, implantable equipment may be connectedto screw 200, such as components of a spinal rod system, such as one ofthe systems mentioned above. Over time, bone may grow into the porousstructure 226, 227 of screw 200 helping to further secure screw 200 tothe bone. If after a such ingrowth occurs, it is necessary to removescrew 200 from the bone via a revision procedure or the like, screw 200may be reengaged with a driver instrument and rotated such that thebonds formed between screw 200 and bone via bone ingrowth are brokenthereby allowing screw 200 to be removed without the need to cut excessbone surrounding the screw for its removal.

FIG. 3 depicts a screw 300 according to a further embodiment of thepresent disclosure. Screw 300 includes a head 310 and screw portion 320extending from head 310. Head 310 is a tulip-shaped head that includes aU-shaped slot 314 extending through head 310 and transverse to an axisof screw 300. Such slot 314 is configured to receive a spinal rodtherein and may be internally threaded for threaded engagement to a setscrew (not shown) or the like, as disclosed in U.S. Pat. No. 8,007,520,the disclosure of which is incorporated by reference herein in itsentirety. Head 310 also includes a proximal solid portion 311 and adistal porous portion 312. Distal porous portion 312 comprises a distalend of head 310 adjacent to screw portion 320 of screw 300. In thisregard, distal porous portion 312 defines a distally facing surface sothat when screw 300 is driven into bone, porous portion 312 sitsdirectly against the bone, such as a transverse process/facet junction.In the embodiment depicted, distal porous portion 312 forms a ring thatextends about the axis of screw 300 and has a proximal-distal length ofabout 0.5 to 2 mm, but preferably 1.75 mm. In addition, distal porousportion 312 does not extend full thickness through head 310 and insteadpreferably extends into head 310 from the exterior thereof. In thisregard, the entire internal surface 316 of head 310 is solid. Thedistance into which the porous portion 312 extends into head 310 may beabout 0.3 to 0.8 mm, but preferably 0.5 mm. In addition, this distanceor thickness of porous portion may vary along the proximal-distal lengthof porous portion 312 to account for regions of high stress. However, insome embodiments porous portion 312 may span full thickness betweeninner surface 316 and an exterior of tulip-shaped head 310, such thatporous portion 312 comprises a portion of internal surface 316. Also,screw portion 320 may be similar to screw portion 120 with the exceptionthat screw portion 320 may be entirely solid.

In a method of use, a driver is engaged to screw 300, and screw 300 isdriven into bone, such as a vertebrae. Once fully seated, distal porousportion 312 is positioned directly against the bone. In this regard, thebone, such as a transverse process/facet junction, may be abraded beforescrew insertion so that porous portion 312 directly abuts the abradedbone to help facilitate bone ingrowth. Implantable hardware may then beconnected to the screw 300. For example, a spinal rod may be insertedinto slot 314 such that it extends therethrough in a directiontransverse to an axis of screw 300. A set screw may then be threaded tohead 310 over the spinal rod for securing rod to screw 300. Over time,bone may grow into porous portion 312 of screw 300 helping to furthersecure screw 300 to the bone. If after such ingrowth occurs, it isnecessary to remove screw 300 from the bone via a revision procedure orthe like, all hardware may disengaged from screw 300. Screw 300 may thenbe reengaged with a driver instrument and rotated such that the bondsformed between distal porous portion 312 and bone via bone ingrowth arebroken thereby allowing screw 300 to be removed without the need to cutexcess bone surrounding screw 300 for its removal.

FIG. 4 depicts a bone screw 400 according to an even further embodimentof the present disclosure. Screw 400 is a lag screw and has a head 410,first screw portion 420 a, second screw portion 420 b, and shank 430.Screw 400 may be used with other orthopedic devices, such as boneplates, or by itself. First screw portion 420 a is positioned adjacenthead 410 while second screw portion 420 b is positioned at a distal endof screw 400. Screw 400 may be cannulated, like screw 200, or notcannulated. First and second screw portions 420 a-b are threaded andhave a solid structure.

Shank 430, which is disposed between first and second screw portions 420a-b, is unthreaded and includes a solid exterior surface 434 that isinterrupted by a plurality of porous fenestrations 432 arrayed aboutshank 430. Fenestrations 432 are similar to fenestrations 226 of screw200 in that they are organized in a helical pattern with a fenestration432 positioned every 10 to 90 degrees, but preferably every 20 degreesabout shank 430. However, in some embodiments, fenestrations 432 may bearranged in a non-helical pattern, such as in linear rows. Moreover,fenestrations 432 may extend through shank 430 such that theycommunicate with a channel (not shown) for aspiration of bone marrowaspirate or for delivery of a flowable material to the bone. This may befacilitated by one or more porous liners lining the channel, such asporous liners 227 of screw 200. However, in some embodiments,fenestrations 432 may not extend entirely through shank 430 to thechannel or may have fenestrations 432 that communicate with the channeland some that do not. However, where fenestrations 432 do not extendthrough shank 430 to the channel, fenestrations preferably extend 0.5 mmor greater through the exterior of shank 430.

Fenestrations 432 are shown as defining a round opening, which may havea diameter of 0.5 to 1.2 mm, but preferably 1 mm. Moreover, eachfenestration 432 may have the same diameter, or, in some embodiments,fenestrations 432 may have a variable diameter such that some of thefenestrations 432 have a smaller diameter than other fenestrations 432.For example, some of fenestrations 432 may have a diameter of 0.5 mmwhile others may have a diameter of 1 mm. While fenestrations 432 areshown as defining a round, porous opening in the solid structure ofshank 430, fenestrations 432 can define other shaped openings such as asquare, ovular, or triangular shaped opening, for example.

FIG. 5 depicts a bone screw 500 according to yet another embodiment ofthe present disclosure. Screw 500 is similar to that of screw 400 withthe exception that shank 530 is entirely porous rather than havingporous portions arrayed within a solid exterior. In this regard, screw500 has a solid head 510, a solid first screw portion 520 a, a solidsecond screw portion 520 b, and a porous shank 530 disposed betweensolid screw portions 530 a-b. Porous shank portion 530 may have uniformporosity throughout the thickness of shank 530. However, in otherembodiments, the porosity may increase in a radial direction from anaxial center of screw. In even further embodiments, shank 530 may not beentirely porous. Instead, the porous structure may extend inward towardthe axis of screw 500 about 0.5 mm or greater from an exterior of shank530 while the core of shank 530 may be a solid, cylindrical structurewhich underlies the porous structure of shank 530. In embodiments wherea channel extends through screw 500 similar to channel 130 of screw 100,such solid core of shank may form a hollow, cylindrical structure.

The exemplary screws described herein may be formed layer-by-layer usingan additive layer manufacturing (ALM), i.e., 3D printing, process so noseparate connection mechanism is necessary to bring together any of thecomponents of such bone screws. In some examples, ALM processes arepowder-bed based and involve one or more of selective laser sintering(SLS), selective laser melting (SLM), and electron beam melting (EBM),as disclosed in U.S. Pat. Nos. 7,537,664; 8,728,387; 9,180,010; and9,456,901, the disclosures of which are hereby incorporated by referencein their entireties herein. Assembly of a bone screw with solid andporous portions using ALM is discussed in greater detail below

In some arrangements, the above described bone screws are formed usingan ALM fabrication process, such as SLS, SLM or EBM described above,fused deposition modeling (FDM), or other appropriate 3D printingtechnologies known to those skilled in the art. When employingpowder-bed based technologies, articles are produced in layer-wisefashion according to a predetermined digital model of such articles byheating, e.g., using a laser or an electron beam, multiple layers ofpowder, which preferably may be a metallic powder, that are dispensedone layer at a time. The powder is sintered in the case of SLStechnology and melted in the case of SLM technology, by the applicationof laser energy that is directed in raster-scan fashion to portions ofthe powder layer corresponding to a cross section of the article. Afterthe sintering or melting of the powder on one particular layer, anadditional layer of powder is dispensed, and the process repeated, withsintering or melting taking place between the current layer and thepreviously laid layers until the article is complete. The powder layerssimilarly may be heated with EBM technology. Additive manufacturingtechniques such as the ALM processes described above may be employed toform the solid and porous layers and any other components, asapplicable. In some instances, materials for one layer may be differentthan the materials for successive layers. This process allows for porousportions to extend full thickness through a particular structure, suchas the thread 122 of screw 100 and the shank 530 of screw 500, forexample. It also allows porous portions to be formed in locationsimpossible to reach by other methods, such as the liners 227 of screw200 which are located about channel within screw 200.

Each of solid and porous layers of the above described screws may beconstructed from biocompatible metals, such as titanium, titaniumalloys, stainless steel, cobalt chrome alloys, tantalum, niobium,another metal, or a biocompatible polymer, such as polyether etherketone (PEEK). All constituent porous and solid portions of the abovedescribed screws may be a common material, such as one of those listedabove, or different materials can be employed for each part. Particularcombinations of materials and their use for specific parts of hereindescribed bone screws are a matter of design choice and may include thecombination of different metals, different polymers, or metals combinedwith polymers. For example, the solid portions of the herein describedscrews can be made from a metal while the porous portions may be madefrom a polymer.

Each of the screws describe herein may have other features that mayenhance the function of the screw from those described herein. Forexample, each of the screws described herein may include serrations ontheir respective threads. Examples of such serrated threads aredescribed in U.S. appln. Ser. No. 15/645,264, the disclosure of which ishereby incorporated by reference in its entirety.

Moreover, each of the screws described above are not limited to theparticular porous and solid configurations described above. Indeed, eachof the above screws can have alternative solid/porous configurationsand/or combinations as those previously described. For example, screw100 may also include the fenestrations 226 described with respect toscrew 200. In such an embodiment, thread 122 may have a solid and porousstructure as described with relation to screw 100 while also havingporous fenestrations distributed in a helical array between thread 122as described with relation to screw 200. In another example, screw 300may include the solid/porous thread 122 of screw 100 and/or porousfenestrations 226 of screw 200 in addition to having the porous ring 312of tulip-shaped head 310.

Also, while the above described solid/porous configurations areassociated with particular bone screws, it should be understood that thedescribed solid/porous configurations can be applied to any generalpurpose bone screw or other specialized bone screws not describedherein. Examples of such screws are disclosed in U.S. Pat. No. 6,974,460and U.S. Publication No. 2017/0086887, the disclosures of which arehereby incorporated by reference herein in their entirety. Moreover, thesolid/porous configurations are not limited to screws used in spinalprocedures.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. A bone fastener, comprising: a head; a screw portion extending fromthe head, the screw portion having a shaft and a thread extendinghelically along and about the shaft and defining a helical depressiontherebetween; and a plurality of porous fenestrations disposed withinthe helical depression and extending into the shaft, the porousfenestrations being filled with a porous structure configured to promotebone ingrowth, the porous structure comprising a portion of an externalsurface of the bone fastener and being surrounded by a solid structurehaving a porosity smaller than that of the porous structure; and aporous liner at least partially surrounding the channel and beingdisposed within the shaft of the screw portion, the porous liner havinga porous structure interconnected within the porous structure of atleast two of the porous fenestrations.
 2. The bone fastener of claim 1,wherein the porous fenestrations each define a circular opening having adiameter of 0.5 to 1.2 mm.
 3. The bone fastener of claim 1, whereinporous fenestrations extend into the shaft 0.5 mm or greater.
 4. Thebone fastener of claim 1, further comprising a channel extending alongthe length of the bone fastener and through both the screw portion andhead of the bone fastener.
 5. The bone fastener of claim 3, wherein atleast some of the porous fenestrations extend through the shaft and intocommunication with the channel such that the porous structure extendsfrom the channel to an exterior of the bone fastener.
 6. The bonefastener of claim 1, wherein each porous fenestration is offset from anadjacent porous fenestration by 10 to 90 degrees about a longitudinalaxis of the bone fastener.
 7. The bone fastener of claim 1, wherein eachporous fenestration is offset from an adjacent porous fenestration by 20degrees about a longitudinal axis of the bone fastener.
 8. A bonefastener comprising, comprising: a head; a screw portion extending fromthe head and having a shaft and a thread extending helically about andalong the shaft and defining a helical depression therebetween; and achannel extending through the shaft and head, wherein the thread is madeof a first material, and the shaft is made of the first material and asecond material such that the second material forms columns arrangedwithin the helical depression and each being surrounded by the firstmaterial and extending from an outer surface of the shaft to thechannel, the second material having a porosity greater than that of thefirst material.
 9. The bone fastener of claim 8, wherein each column hascircular shape at the outer surface of the shaft.
 10. The bone fastenerof claim 8, wherein column is offset from an adjacent column by 10 to 90degrees about a longitudinal axis of the bone fastener.
 11. The bonefastener of claim 8, wherein each porous fenestration is offset from anadjacent porous fenestration by 20 degrees about a longitudinal axis ofthe bone fastener.
 12. The bone fastener of claim 8, wherein the secondmaterial of the shaft further forms a liner extending at least partiallyabout and in communication with the channel.
 13. The bone fastener ofclaim 12, wherein at least a first and second column of the columnsintersects the liner.
 14. The bone fastener of claim 12, wherein theliner is surrounded by the first material.
 15. The bone fastener ofclaim 14, wherein the liner is cylindrical.